The patch titled
Subject: fs/proc: don't expose absolute kernel addresses via wchan
has been added to the -mm tree. Its filename is
fs-proc-dont-expose-absolute-kernel-addresses-via-wchan.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-proc-dont-expose-absolute-kernel-addresses-via-wchan.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-proc-dont-expose-absolute-kernel-addresses-via-wchan.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Ingo Molnar <mingo@xxxxxxxxxx>
Subject: fs/proc: don't expose absolute kernel addresses via wchan
wchan leaks absolute kernel addresses to unprivileged user-space, of
kernel functions that sleep:
static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
unsigned long wchan;
char symname[KSYM_NAME_LEN];
wchan = get_wchan(task);
if (lookup_symbol_name(wchan, symname) < 0) {
if (!ptrace_may_access(task, PTRACE_MODE_READ))
return 0;
seq_printf(m, "%lu", wchan);
} else {
seq_printf(m, "%s", symname);
}
return 0;
}
So for example it trivially leaks the KASLR offset to any local attacker:
fomalhaut:~> printf "%016lx\n" $(cat /proc/$$/stat | cut -d' ' -f35)
ffffffff8123b380
Most real-life uses of wchan are symbolic:
ps -eo pid:10,tid:10,wchan:30,comm
and procps uses /proc/PID/wchan, not the absolute address in
/proc/PID/stat:
triton:~/tip> strace -f ps -eo pid:10,tid:10,wchan:30,comm 2>&1 | grep wchan | tail -1
open("/proc/30833/wchan", O_RDONLY) = 6
These days there's very little legitimate reason user-space would be
interested in the absolute address. The absolute address is mostly
historic: from the days when we didn't have kallsyms and user-space procps
had to do the decoding itself via the System.map.
So this patch sets all numeric output to 0 and keeps the symbolic output
in /proc/PID/wchan.
( The absolute sleep address can generally still be profiled via
perf, by tasks with sufficient privileges. )
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Kostya Serebryany <kcc@xxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20150930071537.GA19048@xxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/array.c | 6 ++----
fs/proc/base.c | 7 +------
2 files changed, 3 insertions(+), 10 deletions(-)
diff -puN fs/proc/array.c~fs-proc-dont-expose-absolute-kernel-addresses-via-wchan fs/proc/array.c
--- a/fs/proc/array.c~fs-proc-dont-expose-absolute-kernel-addresses-via-wchan
+++ a/fs/proc/array.c
@@ -375,7 +375,7 @@ int proc_pid_status(struct seq_file *m,
static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task, int whole)
{
- unsigned long vsize, eip, esp, wchan = ~0UL;
+ unsigned long vsize, eip, esp;
int priority, nice;
int tty_pgrp = -1, tty_nr = 0;
sigset_t sigign, sigcatch;
@@ -454,8 +454,6 @@ static int do_task_stat(struct seq_file
unlock_task_sighand(task, &flags);
}
- if (permitted && (!whole || num_threads < 2))
- wchan = get_wchan(task);
if (!whole) {
min_flt = task->min_flt;
maj_flt = task->maj_flt;
@@ -507,7 +505,7 @@ static int do_task_stat(struct seq_file
seq_put_decimal_ull(m, ' ', task->blocked.sig[0] & 0x7fffffffUL);
seq_put_decimal_ull(m, ' ', sigign.sig[0] & 0x7fffffffUL);
seq_put_decimal_ull(m, ' ', sigcatch.sig[0] & 0x7fffffffUL);
- seq_put_decimal_ull(m, ' ', wchan);
+ seq_puts(m, " 0"); /* Used to be numeric wchan - replaced by /proc/PID/wchan */
seq_put_decimal_ull(m, ' ', 0);
seq_put_decimal_ull(m, ' ', 0);
seq_put_decimal_ll(m, ' ', task->exit_signal);
diff -puN fs/proc/base.c~fs-proc-dont-expose-absolute-kernel-addresses-via-wchan fs/proc/base.c
--- a/fs/proc/base.c~fs-proc-dont-expose-absolute-kernel-addresses-via-wchan
+++ a/fs/proc/base.c
@@ -430,13 +430,8 @@ static int proc_pid_wchan(struct seq_fil
wchan = get_wchan(task);
- if (lookup_symbol_name(wchan, symname) < 0) {
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return 0;
- seq_printf(m, "%lu", wchan);
- } else {
+ if (!lookup_symbol_name(wchan, symname))
seq_printf(m, "%s", symname);
- }
return 0;
}
_
Patches currently in -mm which might be from mingo@xxxxxxxxxx are
fs-proc-dont-expose-absolute-kernel-addresses-via-wchan.patch
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